docs(webpack): fix spelling error (#3030)

Author: paulinoj

public/docs/ts/latest/guide/webpack.jade

@@ -61,7 +61,7 @@ a(id="entries-outputs")
 
 :marked
   Here it sees that we're importing *@angular/core* so it adds that to its dependency list for (potential) inclusion in the bundle.
-  It opens *@angular/core* and follows _its_ network of `import` statements until it has build the complete dependency graph from `app.ts` down.
+  It opens *@angular/core* and follows _its_ network of `import` statements until it has built the complete dependency graph from `app.ts` down.
 
   Then it **outputs** these files to the `app.js` _bundle file_ designated in configuration: